In some respects, the alleged mass murderer in Aurora, Colo. fits a profile of the typical mass killer that my colleague James Alan Fox and I developed some 30 years ago.

In all likelihood, the Colorado killer was depressed and socially isolated, having no place to turn when he got into trouble. In addition, he likely blamed everybody but himself for his personal problems and had access to and training in the use of semi-automatic firearms.

Yet the perpetrator of the Aurora massacre also differs from most other mass killers in important ways.